Abnormality monitoring apparatus for a pipeline

ABSTRACT

In an abnormality monitoring apparatus of the present invention, a plurality of detectors (13, 14) are arranged at a plurality of positions in the axial direction of a pipeline (11) to detect respective sound waves (37) propagating from a position (B) of occurrence of abnormality. The aforementioned position is calculated from a sound wave detection time difference between the detectors (13, 14) and position between the detectors (13, 14). The apparatus further includes an abnormal waveform memory unit (28) for storing the waveforms of a plurality of kinds of typical abnormal sound waves generated from abnormality on the pipeline (11). A display device (19) displays, on the same image screen, the abnormal waveform stored in the abnormal waveform memory unit and that of the sound wave detected. It is, therefore, possible for a monitoring personnel to readily identify a kind of abnormality occurred.

TECHNICAL FIELD

The present invention relates to an abnormality monitoring apparatus formonitoring the occurrence of abnormality, such as an injury and leakage,on a pipeline and, in particular, to an abnormality monitoring apparatusincluding a plurality of detectors arranged at a plurality of placesrelative to the pipeline to rapidly and accurately detect the occurrenceand position of an abnormal spot on the pipeline from a remote site.

The present apparatus includes a plurality of detectors arranged on apipeline to readily identify the kind of abnormality on the pipeline,using the waveforms of sound waves detected by the detectors.

BACKGROUND ART

A pipe of pipeline is usually laid beneath the surface of the ground,buried at a location between the walls of the adjacent buildings, orarranged in a place readily inaccessible by a maintenance personnel.There sometimes occurs an abnormal spot or an injury on the pipe uponimpact from an external force or a leakage of an internal fluidresulting from a corroded pipe wall. It is very cumbersome or difficultto detect occurrence of abnormality on the pipe and locate it once thepipe has been buried or laid beneath the ground surface.

Published Unexamined Japanese Patent Application No. 60-49199 disclosesa piping buried with an optical fiber spirally wound thereon. Thisoptical fiber is connected at one end to a light emitting element and atthe other end to a light receiving element, time differentiatingcircuit, alarm circuit, etc. A light signal emitted from the lightemitting element is transmitted via the optical fiber to the lightreceiving element where it is converted to an electric signal, which isdifferentiated by the time differentiating circuit. An external lateralforce on the buried piping causes microbends on the optical fiber. Thisleads to a greater transmission loss across the full length of theoptical fiber and an abrupt variation in the output signal of the timedifferentiating circuit. The occurrence of abnormality is thus detected.

A piping, if newly buried beneath the ground surface, may be so done ata desired location with the wound optical fiber disposed on the piping.If, on the other hand, an optical fiber cable is provided on an alreadyburied piping, digging-out has to be done at a location around thepiping, involving an unpractically larger construction work expense.

The digging is effective to the situation in which the piping isdeformed over a certain ground area due to the occurrence of earthquake,local ground subsidence or upheaval, etc., but a local impact by anexcavating machine, etc., on the piping and resultant occurrence of ainjured spot or spots on the piping do not correspond to the location ofthe optical fiber cable, sometimes failing to positively detect theoccurrence of abnormality on the optical fiber.

DISCLOSURE OF INVENTION

A first object of the present invention is to provide an abnormalitymonitoring apparatus for readily, rapidly and accurately detecting theoccurrence of abnormality on a pipeline and its position from a localsite.

A second object of the present invention is to provide an abnormalitymonitoring apparatus for readily identifying a kind of abnormality on apipeline.

A third object of the present invention is to provide an abnormalitymonitoring apparatus for readily, rapidly and accurately detecting theoccurrence of abnormality on a pipeline and its position and a kind ofabnormality from a remote site.

In order to achieve the first object of the present invention, aplurality of detectors are arranged at a plurality of places in theaxial direction of a pipeline with a predetermined distance left betweenthe detectors to detect sound waves generated due to the presence ofabnormality on the pipeline and propagating from the position ofoccurrence of abnormality with a fluid as a medium. A sound wavedetection time difference between the detectors is found, for example,at a data processing unit where it calculates the position of occurrenceof abnormality on the basis of the sound wave detection time differenceand distance between the detectors.

In the present apparatus, the respective detector is comprised of a pairof sound wave sensors arranged in the axial direction of the pipelinewith a very small interval left between the paired sound wave sensors.Further, the data processing unit calculates respective sound velocitiesat the positions of the respective detectors on the basis of a soundwave detection time difference between the paired sound wave sensors inthe respective detectors. The respective distances from the positions ofthe respective detectors to the abnormality occurrence position arecalculated using the calculated sound velocities, distance between thedetectors and a sound wave detection time difference between thedetectors.

In the present apparatus thus arranged, if any abnormality occurs atsome place in the axial direction of, for example, a pipeline, acorresponding sound wave is generated and propagates in both thedirections of the pipeline. The provision of respective detectors, forexample, in the neighborhood of both ends of the pipeline enables therespective detectors to detect any abnormal sound on the pipeline. Sincethe distance between the detectors is already known, the position ofoccurrence of abnormality can be located from the sound wave detectiontime difference of abnormal sounds at the respective detectors, providedthat the sound propagating velocity is given. When sound waves aredetected at exactly the same time, it is found that the position ofoccurrence of abnormality is located at an intermediate position betweenthe detectors.

Generally, the velocity of a sound wave propagating in the pipelinevaries depending upon the direction in which the fluid flows through thepipeline, that is, a high speed is involved when the sound wavepropagates in the same direction as that in which the fluid flows and alow speed is involved when the sound wave propagates in a directionopposite to that in which the fluid flows. Therefore, the respectivedistances from the positions of the respective detectors to the positionof occurrence of abnormality on the pipeline can be exactly calculatedas the abnormality occurrence position, using the respective soundvelocity at the respective detector.

In order to achieve the object of the present invention, the presentapparatus comprises the detectors as set out above, abnormal waveformmemory unit for storing the waveforms of abnormal sound wavescorresponding to a plurality of kinds of typical abnormality, anddisplay device for displaying, on the same image screen, the waveformdetected at the detector and waveform of the respective abnormal soundwave read out of the abnormal waveform memory unit.

It is usually possible to initially presume kinds of typical externalforces on, for example, a pipeline or piping buried in the ground. Thatis, the kinds of abnormality are often identified from the kinds ofconstruction works done against the buried piping. From this viewpoint,the abnormal waveform memory unit initially stores the waveforms ofabnormal sound waves as generated from a plurality of kinds of typicalabnormality. Since the display device displays the waveform of arespective abnormal sound and that of sound waves detected at thedetectors, the monitoring personnel can readily identify the kind ofabnormality by comparing both the waveforms displayed on the displaydevice.

The frequency passband for the waveform of the detected sound wave isrestricted using a bandpass filter whose frequency passband is set to200 to 500 Hz. That is, for the frequency passband of less than 200 Hz,the noise of the fluid provides a bar to the reception of a signal and,for the frequency passband exceeding 500 Hz, a signal cannot be detecteddue to too great a propagation loss and, further, the S/N ratio islowered due to the noise originating from the apparatus, etc.

Since the bandpass filter is comprised of a plurality of kinds of unitbandpass filters, it is possible to optionally select a frequencypassband against the waveform of a detected sound wave and hence todisplay the waveform of a sound wave in the form of the mostcharacteristic waveform. The monitoring personnel can readily identifythe kind of abnormality to which the waveform of the sound wave belongs.

In order to achieve the third object of the present invention, aplurality of detectors are arranged at a plurality of places in theaxial direction of the pipeline with a predetermined distance leftbetween the detectors and can detect a respective sound wave generateddue to the occurrence of abnormality on the pipeline and propagatingfrom the position of occurrence of abnormality with a fluid as a medium.For example, a data processing unit finds a sound wave detection timedifference between the detectors and calculates the position ofoccurrence of abnormality on the basis of the sound wave detection timedifference and distance between the detectors.

Further the present apparatus includes an abnormal waveform memory unitfor storing the waveforms of an abnormal sound waves corresponding to aplurality of kinds of typical abnormality and a display device fordisplaying, on the same image screen, the waveform of a sound wavedetected at the respective detector and the respective abnormal waveformread out of the abnormal waveform memory unit.

When there occurs abnormality on the pipeline, the present apparatuscalculates a respective distance from the respective detector to theposition of occurrence of abnormality. The display device displays thewaveform of a sound wave generated due to the occurrence of abnormalitydetected and typical waveforms of abnormal sounds. It is possible forthe monitoring personnel to readily locate the position of occurrence ofabnormality and readily identify the kind of abnormality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a principle of operation for calculating theposition of occurrence of abnormality by an abnormality monitoringapparatus according to one embodiment of the present invention;

FIG. 2 is a model generally showing an arrangement of the abnormalmonitoring apparatus;

FIG. 3A shows a waveform diagram before the passage of a sound wavethrough a bandpass filter in the abnormality monitoring apparatus;

FIG. 3B is a waveform diagram after the passage of a sound wave througha bandpass filter in the abnormality monitoring apparatus;

FIG. 4 is a waveform diagram showing respective waveforms after thepassage of sound waves through respective unit bandpass filters in thebandpass filter in the present apparatus;

FIG. 5 is a block diagram diagrammatically showing a data processingunit in the present apparatus;

FIG. 6A is a waveform showing the waveform of a typical abnormal soundwave obtained by the present apparatus;

FIG. 6B is a waveform showing the waveform of another typical abnormalsound wave obtained by the present apparatus;

FIG. 7 is a flowchart showing the operation of the data processing unitin the present apparatus;

FIG. 8 is a view showing the display contents of a display device in thepresent apparatus; and

FIG. 9 is a model diagram generally showing an arrangement of anabnormality monitoring apparatus according to another embodiment of thepresent invention.

BEST MODE OF CARRYING OUT THE INVENTION

An embodiment of the present invention will be explained below withreference to the accompanying drawings.

FIG. 2 is a model view showing a general arrangement of an abnormalitymonitoring apparatus of the present embodiment which monitors anabnormal state of a piping. The present monitoring apparatus is shown asbeing applied to a piping buried beneath the surface of a ground.

A fluid 12, such as a gas, flows through a piping 11, which is buriedbeneath the surface of the ground 10, in a direction as indicated by,for example, A in FIG. 2. A pair of detectors 13, 14 for detecting asound wave are arranged in the piping 11 such that they are spaced aparta distance L in the axial direction of the piping 11. The detector 13 iscomprised of a pair of sound sensors 13a, 13b spaced apart a distance l3in the axial direction of the piping as shown in FIG. 1. The detector 14is similarly comprised of a pair of sound sensors 14a, 14b spaced aparta distance l3 in the axial direction of the piping. The sensor-to-sensordistance l3 is very small compared with the distance between thedetectors 13 and 14.

Even if, in place of sound sensors arranged in the piping 11, vibrationsensors are located on the wall of the piping in a similar way, it isalso possible to detect a sound wave because the pipe wall is vibratedby the sound wave.

A sound wave signal detected by the sound sensors 13a, 13b is supplied,as a sound wave signal a of the detector 13, to a signal synthesizingcircuit 15. A sound wave signal b detected by the sound sensors 14a, 14bis supplied to the signal synthesizing circuit 15 where the sound wavesignals a and b are synthesized into a new sound wave signal. The outputsound wave signal of the signal synthesizing circuit 15 contains foursound waveforms as detected by the sensors 13a, 13b and 14a, 14b of thedetectors 13 and 14. The sound wave signal of the signal synthesizingcircuit 15 is supplied to an amplifier 16 where it is amplified as asound wave signal c. The sound wave signal c of the amplifier 16 issupplied to a bandpass filter 17. The bandpass filter 17 comprises anon-controlling circuit 17a for allowing the input sound wave signal cto pass without being given any frequency restriction and nine unitbandpass filters (hereinafter referred to as unit BPF) 17b wherefrequency passbands are set to different levels. The center frequenciesof the respective frequency passbands of the respective unit BPF's areset, for every 1/3 octane band frequency, over a frequency range 160 Hzto 1 KHz, such as 160 Hz, 200 Hz, 250 Hz, 315 Hz, 400 Hz, 500 Hz, 630Hz, 800 Hz and 1 KHz.

The bandpass filter 17 serves to eliminate those frequency components inthe output sound wave signal c of the amplifier 16 which result from abackground noise inherent to the flow of a fluid 12 through the piping11 and to the operation of a pressure regulator 12.

FIGS. 3A and 3B are waveform diagrams representing sound wave signalsdetected by the detectors 13 and 14, when, in actual practice, aperiodical vibration is exerted on the piping 11, these detectors beinglocated in a position 5 Km distance from that in which an abnormal stateoccurs. That is, FIG. 3A shows a sound wave signal c after it is outputfrom the amplifier 16 but before it is input to the bandpass filter 17and FIG. 3B shows a sound wave signal d output from the unit BPF 17 withthe center frequency of the frequency passband set to 250 Hz in whichcase the frequency passband of the bandpass filter 17 was set to 200 to500 Hz. From FIGS. 3A and 3B it will be appreciated that, for the soundwave signal c before being input to the bandpass filter 17, a noisewaveform corresponding to the background noise produced due to the flowof the fluid 12 is superimposed over the sound waveform generated uponvibration impact but that a sound wave signal d output from the bandpassfilter 17 contains only a sound waveform generated upon vibrationimpact, not the noise components of the background noise resulting fromthe flow of the fluid 12.

Since kinds of construction machinery have been known which usuallycause a damage to a piping under the surface of the ground in the civilengineering works. In the case where the piping 11 suffers a vibrationimpact during the use of the machinery, it is possible to estimate theproperty of a sound wave propagating in the piping upon vibrationimpact. The frequency of that sound wave is of the order of 200 to 500Hz. Of the frequency components of the sound wave received, only thoseof the aforementioned frequency band range can be passed and the othernoise components be eliminated, largely improving an S/N ratio. For thefrequency bandpass of less than 200 Hz, the fluid noise offers a bar tothe reception of a signal of interest. For the frequency bandpassexceeding 500 Hz, a signal involved cannot be detected due to an excesspropagation loss and, further, the S/N ratio is lowered due to a noisecaused by, for example, the machinery,

FIG. 4 shows a comparison between the output sound waveform of thenon-controlling circuit 17 and the respective sound waveform of therespective unit BPF 17b with the frequency passband so set as set outabove, the non-controlling circuit 17a imposing no restriction to thepassage of a frequency.

Since the attenuation characteristic of the sound wave propagating inthe piping 11 varies depending upon the propagating distance andfrequency, it is difficult to unconditionally determine those passedfrequencies of the whole bandpass filter 17 for obtaining an optimal S/Nratio. However, a sound wave resulting from an abnormal state on and inthe piping can be positively detected, in spite of its source and itspropagating distance, by selecting an optimal one of a plurality of unitPBFs 17b of different frequency passbands each.

In the underground piping through which a gas passes, for example, thefrequency passband is optimally 200 to 500 Hz, but, in the oil pipeline,etc., in the field, the frequency passband becomes a broader range of200 to 2 KHZ optimally because the pipeline 11 sometimes undergoes adirect impact. In this situation, a measuring bandpass may be madebroader by increasing the number of unit BPFs 17b.

Respective sound wave signals d which are output from thenon-controlling circuit 17a and BPF's 17b in the bandpass filter 17 aresupplied to a data processing unit 18 comprised of, for example, amicrocomputer. The data processing unit 18 subjects received soundsignals d to various data proceedings to determine whether or not anyabnormal state occurs on the piping and, when the abnormal state occurs,calculates the position where it occurs.

The data processing unit 18 enables the detected sound signals d,presence or absence of the abnormal state, the location of that state,and the kind of abnormality judged by a monitoring personnel to bedisplayed, if required, on a display device 19 using, for example, a CRTdisplay, and to be transmitted to a central monitoring device 21 via adata transmission device 20. Upon receipt of any abnormality occurrenceinformation, the central monitoring device 21 informs it, together withits location and its kind, and gives an alarm via an alarm device 22, toanother monitoring personnel.

The data processing unit 18 is so constructed as shown in FIG. 5. Therespective sound signals d of the non-controlling circuit 17a and BPF's17b in the bandpass filter 17 are converted by a LOG (logarithm)converter 23 to a decibel value (dB). The values of the converter 23,after being sampled with a given frequency, are converted by an A/Dconverter 24, to a digital sound wave signal e. The respective digitalsound wave signals are supplied to a multiplexer circuit 25. Amultiplexer circuit 25 receives the respective digital sound wavesignals e in the same timing and sends them to a bus line 25.

To the bus line 25 are connected a CPU (central processing unit) 26 forperforming various calculation proceedings, ROM 27 stored with variousfixed data, such as a control program, abnormal waveform memory unit 28,such as a ROM, stored with a plurality of kinds of typical abnormalwaveforms, RAM 29 for temporarily storing various variable dataassociated with the abnormality occurrence position calculation, and areadout wave memory 30 temporarily stored with the wavelengths of therespective sound signals d which are read through the multiplexercircuit 25. To the bus line 25 are further connected a timer circuit 31for controlling the readout time intervals T_(M) of the sound wavesignals e, keyboard circuit 33 for entering key signals as variousoperation instructions from a keyboard 32 by the monitoring personnel,I/O interface 34 for sending various kinds of transmission data to thedata transmission device 20, I/O interface 35 for sending variousdisplay data to the display device 19.

The abnormal wavelength memory unit 28 stores respective typicalabnormal waveforms as shown, for example, in FIGS. 6A and 6B. That is,FIG. 6A shows the waveform of sounds detected by the detectors 13 and 14when a road surface beneath which the piping 11 is buried isperiodically dug out by a back hoe- FIG. 6B shows a sound waveformdetected by detectors 13 and 14 when a road surface beneath which thepiping 11 is buried is continuously dug out. The abnormality sometimesoccurs due to the digging out of a construction machine, such as theaforementioned back hoe and vibratory hammer, and to the leakage of afluid resulting from an injured wall of the piping. In this way,different sound waveforms emerge, depending upon the kinds ofabnormality.

The procedure for detecting the occurrence of abnormality caused by animpact of the vibratory hammer's tip 36 against a spot on the outersurface of the piping 11 will be explained below with reference withFIG. 1.

when an impact is applied to the outer surface of the piping 11, then asound wave 37 is transmitted through the piping 11 with a fluid 12 as amedium, and propagates in the directions of the detectors 13 and 14. Inthe case where the fluid 12 flows in the direction A, the velocity(propagation velocity) V1 of sound propagating in the direction of thedetector 14 is greater than the sound velocity (propagation velocity) V2of sound propagating in the direction of the detector 13.

Given that ΔT14 represents a time difference detected by the pair ofsound wave sensors 14a, 14b in the detector 14, the sound velocity V1 isgiven by

    V1=l3/ΔT14                                           (1)

where l3 represents the distance between the sound wave sensors 14a and14b.

Similarly, the velocity V2 is given by

    V2=l3/ΔT13                                           (2)

where

ΔT13 represents a time difference detected by the pair of sound wavesensors 13a, 13b in the detector 13.

With t1, t2 representing the times at which respective sound waves 37are detected by the detectors 14 and 13,

    ΔT=t1-t2                                             (3)

where ΔT denotes a difference at times t1 and t2 at which the sounds aredetected at the detectors 14 and 13 as actually detectable values.

In Equation (3), the sound wave detection time difference ΔT becomespositive when the detector 13 detects the sound wave 37 earlier than thedetector 14. Through a simpler consideration, the distances l1 and l2from an abnormal spot B to the detectors 14 and 13 can be found fromEquations (4) and (5) given below

    l1=V1 (L+ΔT·V2)/(V1+V2)                     (4)

    l2=V2 (L-ΔT·V1)/(V1+V2)                     (5)

The abnormal spot B can be found by calculating Equations (4) and (5) bythe data processing unit 18.

CPU 26 in the data processing unit 18 is program-designed that, uponreceipt of an interrupt signal from the timer circuit 31 for everyread-out time interval T_(M), it executes a determination supportprocessing for determining the presence or absence of any abnormal spot,its position and its kind in accordance with a flowchart shown in FIG.7.

When a time interrupt signal is input from the timer circuit 31 to CPU18, respective digital sound wave signals e which are output from therespective A/D converters 24 after their original signals pass throughthe non-control circuit 17 and respective BPF's 17b in the bandpassfilter 17 and then through the respective LOG converters 23 are readinto CPU 18 through the multiplexer circuit 25 for a predetermined timeT corresponding to time necessary for waveform analysis (step S1). Thewaveforms of the read-in sound wave signals e are stored in the readoutwaveform memory 30 at step S2.

At step S3, the S/N ratios of the respective sound waveforms stored inthe readout waveform memory 30 are evaluated through the use of astatistical procedure for finding, for example, an autocorrelationfunction - step S3. At step S4, CPU reads out a signal level h atrespective times of the sound waveforms corresponding to an evaluatedmaximal S/N ratio.

At step S5, the sound waveform corresponding to the read-out maximal S/Nratio is displayed on a display device 19. Further, a maximal value ofthe signal level h at the respective time position is retrieved. If themaximal value of the signal level h detected does not exceed apredetermined restrictive value at step S6, CPU 26 determines that thereis no abnormal waveform and displays a massage on display device 19indicating that there is no abnormal state on the piping - step S7.

Further, when the maximal value of the signal level exceeds arestrictive level, CPU determines that there occurs an abnormal state onthe piping. Control goes to step S8. At step S8, CPU detects four timepositions corresponding to abnormal sound waveforms generated uponimpact on the piping and detected out of the sound waveforms a1, b1 bythe sound wave sensors 13a, 13b and 14a, 14b of the detectors 13 and 14,respectively.

At step S9, CPU calculates, from the detected four time positions, soundwave detection time differences ΔT13, ΔT14 of the respective sound wavesensors and a sound wave detection time difference ΔT of the detectors.At step S10, CPU calculates distances l1, l2 from the abnormal spot B tothe detectors 14 and 13 - step S10.

Upon termination of the position calculation processing on the positionof the abnormal spot on the piping, CPU reads out the respectiveabnormal sound waveforms (see FIGS. 6A and 6B) from the abnormalwaveform memory 28 - step S11. At step S12, CPU reads out a soundwaveform of those respective sound waveforms stored in the readoutwaveform memory 30, that is, a sound waveform corresponding to a soundwave signal d delivered from the non-controlling circuit 17a (a circuitproviding no frequency restriction in the bandpass filter 17), anddisplays it, together with the abnormal sound waveform, on the displaydevice 19. For ease in comparison between the respective soundwaveforms, they are displayed with the same contracted time widthshorter than upon calculation of the distances l1, l2.

If a skip key signal is input from the keyboard 32 through the keyboardcircuit 33, CPU determines the next unit BPF 17b as being selected bythe operator - step S13. At step S14, CPU eliminates the sound waveformof the non-controlling circuit 17a or unit BPF 17b displayed on thedisplay device 19 and then reads out that sound waveform correspondingto the unit BPF 17b of higher frequency passband from the readoutwaveform memory 30 and displays it on the display device 19.

If, at step S15, a key operation for designating the kind of abnormalityis made on the keyboard 32 without operating the skip key, CPU transmitsinformation of abnormality occurrence, its positions l1, l2 and its kindto the central monitoring device 21 via the data transmission unit 20.

If abnormality cannot be determined as belonging to one kind, thenanother key-in operation is effected for another kind of abnormality,

In a sound wave signal d of optimal S/N ratio obtained by eliminatingnoise components from its original signal at the non-controlling circuit17a and respective unit BPF 17b in the bandpass filter 17, CPU measuresa sound wave detection time difference AT represented by the soundwaveforms a1 and b1 corresponding to the sound wave signals a and bdelivered from the detectors 13 and 14, as well as sound wave detectiontime differences ΔT14 and ΔT13 at the sound wave sensors 14a, 14b and13a, 13b in the detectors 14 and 13, as shown in the display device 19in FIG. 1. CPU calculates, from these respective values, soundvelocities V1, V2 at the locations of the detectors 14, 13 and thencalculates final distances l1 and l2 at the abnormal spot B through theuse of the velocities V1 and V2.

If there is no abnormality, the sound wave signals a, b detected at thedetectors 13, 14 contain only those noise components of a backgroundnoise in the fluid 12, not those sound signals of a sound 37 which wouldotherwise be generated due to an abnormal spot on the piping. Thosenoise components, though lower in their level, are eliminated by thebandpass filter 17 and the level of the sound wave signal d input to thedata processing unit 18 is reduced below a restrictive level. In thisway, the data processing unit 18 determines that there occurs noabnormality.

Although the respective sound velocities constantly vary depending uponthe flow direction, flow velocity, component variation and flowvariation of the fluid 12, the abnormality monitoring apparatus of thepresent invention can also measure the sound velocity and largelyenhance the accuracy with which the position of the abnormal spot B iscalculated.

As already set out above, those frequency components of sound waveformsgenerated due to the occurrence of an abnormal spot largely varydepending upon the kinds of abnormality involved. Since the bandpassfilter 17 comprises the non-controlling circuit 17a and plurality ofunit BPF's 17b and selects a sound waveform of a maximal S/N ratio eachtime, it is possible to grasp the presence or absence of abnormality andits spot or position, under the best condition at all times,irrespective of the kinds of abnormality.

If any abnormal spot is produced, it is possible to promptly grasp itsoccurrence or its position. It is also possible to largely improve theaccuracy with which such abnormality is detected, to accurately find theposition of the abnormal spot and to largely improve the reliability ofthe apparatus as a whole, when compared with a system utilizingconventional optical fibers.

Since the detectors 13, 14 are arranged one at each end of the piping11, it is not necessary to dig the ground surface to see where to locatean abnormal spot on the whole length of an underlying piping. Thisoffers a greater saving in construction costs for installing theabnormality monitoring apparatus.

Vibrations caused by an injured spot or spots on the pipe 11 directlypropagate across the thickness of the piping 11. The vibration energysuffers attenuation, such as the earth and sand around the outer surfaceof the piping and corrosion-resistant coating. In view of its greaterattenuation, however, the injured spot cannot be detected on the pipingat a far site and it is only possible to detect it so long as it islocated at near site on the piping.

The energy of a sound wave propagating in the flow of a fluid is notinfluenced by the earth and sand. It has been found that the frequencyband of the order of several Hz to several KHz in particular has theproperty of less damping and involves a greater abnormal sound with anincreasing fluid pressure to enhance a propagation characteristic. Thisenables a sound wave to be transmitted over a long distance. If thedetectors 13 and 14 are provided on the piping with a longer distanceleft as the distance L therebetween, it is possible to monitor anabnormal spot on the greater length of the piping with less number ofdetectors 13 and 14. Monitoring can be achieved for the presence of anabnormal spot on the piping with the detectors set at a distance L ofabout 10 to 15 Km, depending upon the level of a sound wave generateddue to an abnormal site on the piping.

Upon occurrence of any abnormal spot on the piping, the waveform of asound wave 37 propagating in the piping greatly differs in accordancewith the kinds of abnormality. Typical abnormal sound waveforms areinitially stored in the abnormal waveform memory unit 28. Thesewaveforms, together with the waveforms received from the detectors 13and 14, are simultaneously displayed on the display device 19. Themonitoring personnel can make a comparison between the two and readilyinfer which abnormal sound waveform the detected sound waveform belongsto. By doing so, it is possible to readily Judge the kinds ofabnormality.

If the kind of abnormality cannot be identified by a single comparison,a sound waveform passing through the unit BPF 17b corresponding to thenext bandpass frequency is displayed by operating a skip key. Themonitoring personnel can make a similar comparison with a sound waveformof a most typical type or a best S/N ratio displayed on the displaydevice. As a result, the kind of abnormality can promptly and positivelybe identified.

FIG. 9 is a view diagrammatically showing an arrangement of anabnormality monitoring apparatus according to another embodiment of thepresent invention. In this embodiment, the same reference numerals areemployed to designate parts or elements corresponding to those shown inFIGS. 1 and 2 and further explanation is, therefore, omitted.

Generally, a pipeline for petroleum, gas, etc., extends over a distanceof several hundreds of Kms. In the case where a plurality of detectorson the piping 11 are connected to special signal lines, it is necessaryto lay down new signal lines along the piping 11 and hence to spend lotsof memory on them. In this embodiment, associated detectors 13, 14 onthe piping are not connected to each other and, instead, terminaldevices 41 and 42 are provided in the neighborhood of the detectors 13and 14 and have the function of detecting abnormality on the piping. Acentral monitoring device 43 is connected to the respective terminaldevices 41 and 42 through a wireless communication channel or a datacommunication channel to calculate the position of an abnormal spot B onthe piping and determine the kind of its abnormality.

In this embodiment, a pair of sound wave sensors 13a, 13b in thedetector 13 detect sound wave signals a1 and a2 and are input torespective bandpass filters 17 after they have been amplified bycorresponding amplifiers 16 in the terminal device 13 without beingsubjected to signal synthesis. The bandpass filter 17 is of the sametype as that shown in FIG. 5. Respective sound wave signals d are outputfrom a non-controlling circuit 17a and unit BPF's 17b in the respectivebandpass filter 17 to a data processing unit 44. A display device 19 isconnected to the data processing unit 44 comprised of one type ofmicrocomputer. The data processing unit 18, like that shown in FIG. 5,performs data processing on the respective sound wave signals d, thatis, those signals input from the respective bandpass filters 17 withoutbeing subjected to frequency restriction, and on the respectivefrequency-restricted sound wave signals, and determines whether or notthere occurs an abnormal spot on the piping. The data processing unit 44measures, upon occurrence of an abnormal spot on the piping, itsdetection time t1 and calculates a sound velocity V1 from a timedifference ΔT13 at which such abnormality is detected between therespective sound wave sensors 13a, 13b. The calculation is carried outin accordance with the aforementioned procedure. The respective data V1and V1 as well as the respective waveforms of the respective sound wavesignals d delivered from the bandpass filters 17 are transmitted to acentral monitoring device 43 via a data transmission device 45. In thisconnection it is to be noted that, in the absence of any abnormality,nothing is transmitted to the central monitoring device 43.

Sound wave signals b1 and b2 detected by a pair of sound sensors 14a,14b in the other detector 14 are individually amplified by amplifiers 16in the terminal device 42 and input to the bandpass filters 17.Respective sound wave signals d output from the respective bandpassfilters 17 are input to a data processing unit 46. A display device 19is connected to the data processing unit 46. The data processing unit 46performs various data processings on the sound wave signals d input fromthe respective bandpass filters and determines whether or not there isany abnormal spot or spots on the piping. If such abnormality occurs,the data processing unit 46 measures its detection time t2 andcalculates its detection time difference ΔT14 between the sound wavesensors 14a and 14b in accordance with the aforementioned procedure. Thedata t2 and V2, as well as respective waveforms of respective sound wavesignals d output from the respective bandpass filters 17, aretransmitted via a data transmission device 47 to the central monitoringdevice 43. In the absence of any abnormal spot on the piping, nothing istransmitted to the central monitoring device 43.

Respective display devices 19 of the respective terminal devices 41 and42 are not necessarily required and may be omitted.

The central monitoring device 43 is comprised of one type ofmicrocomputer and has a display device 48 and alarm device 49. Thecentral monitoring device 43 calculates, upon receipt of the respectivedata t1, t2, V1, V2 and respective sound waveforms from the respectiveterminal devices 41 and 42, the distances l1 and l2 leading to theposition of an abnormal spot on the piping, by Equations (3), (4) and(5), based on the respective data t1, t2, V1 and V2. The centralmonitoring device delivers information on the generation and position ofthe abnormal spot B to the alarm device 49 to inform the monitoringpersonnel of the occurrence of that abnormality.

The central monitoring device 43 includes an abnormal waveform memoryunit having the same arrangement as the abnormal waveform memory unit 28and storing a plurality of typical abnormal sound waveforms. A displaydevice 48 displays the waveforms of the respective sound wave signals dreceived from the respective terminal devices 41 and 42, that is, thosesound wave signals d, restricted or not restricted by the bandpassfilter 17 in their frequency, as well as the waveforms of the abnormalsounds of known types read out of the abnormal waveform memory unit.Informed of the occurrence of abnormality by the alarm device 49, themonitoring personnel is prompted to determine what kind of abnormalityoccurs on the piping.

In the thus arranged abnormal monitoring apparatus, only the terminaldevices 41 and 42 are arranged at the positions of the detectors 13 and14. The sound waveforms of the sound signals obtained at the terminaldevices 41 and 42, as well as respective data necessary to locate theposition of the abnormal spot B, are transmitted to the centralmonitoring device 43 through a wireless channel. It is only necessary tocheck for the kinds of abnormality at the central monitoring device 43.The monitoring personnel has only to reside in the central monitoringdevice 43, not at the locations of the terminal devices 41 and 42.

In this embodiment, those sound wave signals a1, a2, b1, b2 detected atthe sound wave sensors 13a, 13b, 14a, 14b in the detectors 13, 14 passthrough their own signal processing circuits to the data processingunits 44, 46. Therefore, it is possible to obtain their own independentsound wave signals d. Comparison is made between the sound wave signalsd to gain abnormality detection time differences ΔT13, ΔT14. Since thesound wave signals are not synthesized as shown in FIG. 1, even if thedetection time differences at the respective sound wave sensors 13a,13b, 14a, 14b become smaller due to, for example, the occurrence ofabnormality in a continuous mode, the abnormality detection timedifferences ΔT13 and ΔT14 can positively be detected without causing anoverlap between the adjacent waveforms. Thus, the distance Z3 can bemade smaller with respect to the sound wave sensors 13a, 13b and 14a,14b.

Further, since the sound signals a1, a2, b1, b2 detected at the soundwave sensors 13a, 13b, 14a, 14b are independently input to the dataprocessing units 44, 46, it is possible to readily judge that either oneof the sound sensors has detected an abnormal sound wave earlier thanthe remaining sound sensor. That is, it is possible to more readilyJudge the direction in which an abnormal site on the pipe is located.

The present invention is not restricted to the aforementionedembodiments. Although, in the apparatus of the embodiment, the bandpassfilter 17 has been explained as comprising the non-controlling circuit17a and nine BPF's 17b of different center frequencies at theirfrequency bandpasses, a single bandpass filter may be provided, instead,which has a frequency bandpass of 200 to 500 Hz substantiallycorresponding to the frequency of a sound wave caused by an impact ofvibration and propagating in the piping. The restriction of thefrequency passband can prevent an entrance of a fluid noise (backgroundnoise) of less than 200 Hz which provides a bar to the reception of asignal of interest. For a frequency exceeding 500 Hz, no signal emergesbecause of too great a propagation loss, initially preventing a fall inan S/N ratio resulting from a noise from the apparatus, etc.

Although, in the embodiment, the detectors 13 and 14 are arranged in thepiping 11, they may be arranged on the outer surface of the piping 11since vibration is caused across the tube wall by a sound wavepropagating in the piping 11.

We claim:
 1. An abnormality monitoring apparatus for identifying a typeof abnormality on a pipeline through which a fluid passes,comprising:detector means, arranged in the pipeline, for detecting asound wave generated at a position of occurrence of an abnormality andpropagating with the fluid as a medium; abnormality waveform memorymeans for storing abnormal waveforms of sound waves caused by aplurality of typical abnormalities; a plurality of unit bandpassfilters, having respective different frequency passbands, each foreliminating a noise component generated by the fluid in the pipeline andcontained in the sound wave detected by said detector means, andoutputting a filtered sound wave; and display means for displaying, on asame image screen, a waveform of the filtered sound wave which is outputby at least one of said plurality of unit bandpass filters, and anabnormal waveform read out of said abnormality waveform memory means;and wherein respective frequency passbands of said unit bandpass filtershave center frequencies which are set for each 1/3 octave band frequencywithin a frequency range of from 200 Hz to 500 Hz.